1. Field of the Invention
The present invention relates to a pump and more particularly to an improvement in an auxiliary radially shifting mechanism for vanes in a pump of the vane type.
2. Description of the Prior Art
Hitherto, the pumps of this type have generally had a constitution such as that illustrated in FIGS. 1, 2, and 3 of the drawings in which a rotor 5 fixedly secured to a driving shaft 1 is rotatably received within a cup-shaped cylinder 2 eccentric to the center of the cylinder 2, a number of vanes 7 being disposed within slots 5a (FIG. 2) formed in rotor 5 so as to be radially shiftable, and vanes 7 are adapted to have their radial outer ends abut against the inner periphery of cylinder 2 so that fluid is sucked through a suction port 8 provided in cylinder 2 to be discharged throgh a discharge port 9 also provided in cylinder 2. In the drawings, the reference numeral 3 is a bracket secured to cylinder 2 to sealingly close cylinder 2; 4 is a bearing to rotatably support driving shaft 1 in bracket 3; 6 is a fluid seal to prevent the fluid within cylinder 2 from leaking; and 3a is a ring-shaped projection provided on bracket 3 so as to be concentric with cylinder 2.
The operation of the pump described above is as follows.
As rotor 5 is rotated by means of driving shaft 1 by a prime mover (not shown), centrifugal force is applied to vanes 7 radially shiftably disposed within slots 5a formed in rotor 5 so that they are urged radially outwards in slots 5a, vanes 7 revolving relative to cylinder 2 with their radially outward end portions abutting against the inner periphery of cylinder 2. Due to the constitution as above described, as vanes 7 revolve, the fluid enclosed within fluid delivery chambers 2a and 2b each defined by the inner periphery of cylinder 2, rotor 5 and neighboring vanes 7 is discharged through discharge port 9, new fluid being again sucked through suction port 8, and thus the pump functions as a fluid pump to deliver the fluid under pressure. In this conventional pump, ring-shaped projection 3a, provided on bracket 3 concentric with cylinder 2, acts such that, when the centrifugal force applied to vanes 7 is low as a result of a low rotary speed of rotor 5, it forcefully thrusts vanes 7 radially outwards with respect to rotor 5 so as to cause the radially outward ends of vanes 7 to abut against the inner periphery of cylinder 2 so as to form fluid delivery chambers 2a and 2b.
From the foregoing it will be appreciated that a conventional pump of the vane type having the constitution and the operation described above exhibits such defects that, when the rotational speed of rotor 5 is low and if the viscosity of the fluid to be pumped is high, since ring-shaped projection 3a provided on bracket 3 must always urge vanes 7 radially outwards, the portion of vane 7 which comes into contact with projection 3a wears out to take a configuration with substantially the same curvature as that of projection 3a as the operation time of the pump increases, resulting in a decrease in the mechanical strength of the vanes 7 due to their shape in the worn out configuration and in particular due to their sharp corners.